OF WASHINGTON. 245 



pound eye to a little beyond the base of the labrum. This is the 

 exterior face of the mandible, and when dissected free 'from the 

 adjoining parts is found to consist of this exterior portion, with a 

 flange-like projection apically (II <5), which passes under the la 

 brum. This anterior expansion extends apically in a narrow tongue 

 analogous to the similar projection from the apex of the labrum, 

 and the inner edge of this expansion or tongue is grooved to 

 receive the mandibular seta (II c} which originates in a large, 

 bulbous, fleshy expansion (II ^'), attaching near the base of the 

 mandible interiorly. The mandibular seta? are very much the 

 stouter of the two pairs, and the tips are serrated for a short 

 distance. The exterior face of the mandible, especially apically, 

 is clothed with long hairs. 



Maxilla. Viewed again laterally, and following the man 

 dible, a more elongate sclerite is seen (III #), which expands 

 somewhat apically. On dissecting this out, it is found to be al 

 most identical in general structure with the mandible, having 

 a similar apical expansion (III ), with pseudo-sheath (III' b' 

 Fig. 22), through which the seta (III c) passes, and the bulbous 

 expansion of the seta (III c') which merges into the base of the 

 maxilla. The maxillary seta is much more delicate than the 

 mandibular one, and is simple at tip, though somewhat hooked. 



I have made no effort to homologize the parts of the maxilla 

 just described with the maxilla of biting insects, as the modifica 

 tion in the present case has been so great, in the process of the 

 evolution of the sucking mouth, that any homologies suggested 

 would be largely fanciful. The striking similarity between the 

 upper and lower jaws in the cicada discourages the applying of 

 names to the parts in the maxilla which, in the biting insects, are 

 known only in the maxilla, and in this case would have to apply 

 to both jaws. 



It suggests, however, that in the original or early type of 

 insect mouth, the two pairs of lateral jaws were of similar 

 construction, probably both serving the purpose of biting or 

 gnawing, and that the present wide divergence between the 

 comparatively simple mandible and the very complex maxilla of 

 biting insects is the result of a long line of variation in which 

 the original function of the mandible has been largely retained, 

 while the maxilla has been so modified as to make it an organ 

 adapted to and used for holding and adjusting the food material, 

 rather than for breaking it up or masticating it, and also as an or 

 gan of taste and touch. 



Labium. The labium (IV tf, 3, c} applies directly against 

 the maxillae and forms the floor of the mouth. It is three-jointed, 

 the joints being homologous, probably with the submentum (#), 

 mentum (), and ligula (c) of the biting insect mouth. From the 



